While soybeans provide a high-quality protein, and there are increasing reports of health benefits from consuming soy protein products (FDA, 1999), the demand for soybeans in human foods has not been large. In 1971, less than 1 percent of the U.S. soybean crop was used as a protein source for human foods (Wolf and Cowen, 1971) and today, this value is about the same (SoySource, 1999). This is largely due to the undesirable flavor and odor associated with soy products (Kinsella, 1979; McLeod and Ames, 1988; Wilson et al, 1990; Freese, 1999). Jorge et al. (1999) demonstrated that the introduction of as little as 2% powdered soy milk into chocolate significantly lowered sensory scores with levels above 6% were deemed unacceptable. Incorporating soy protein isolate (SPI) at a level of 2% into frankfurters significantly lowered sensory scores (He and Segranek, 1996). The components that comprise the beany odor of soy products have been thought to include aliphatic carbonyls, volatile fatty acids, amines, alcohols or furans which were derived, in part, from the action of soybean lipoxygenase and subsequent formation of lipid oxidation products (Wolf and Cowan, 1975; Sessa and Rackis, 1977). Much work as been accomplished in recent decades toward developing soybean mutants that lack the lipoxygenase (EC 1.13.11.12) isozymes (L-1, L-2 and L-3) (Kitamura, 1984, Pfeiffer et al, 1992). These mutants allowed Shen et al, (1996) and Shen et al, (1997) to demonstrate that soybean oils prepared from lipoxygenase null soybeans showed no significant improvement in oil stability. Also, soy protein products prepared from lipoxygenase null soybeans still contained significant levels of xe2x80x9cbeanyxe2x80x9d odor (Maheshwari et al, 1997).
Headspace analyzes of unheated and heated SPI employing gas chromatography/mass spectrometry (GC/MS) have been used for examining the volatile components associated with soy proteins (Qvist et al, 1974; del Rosario et al, 1984). However, the contribution of these individual components to the odor of these soy products was not investigated. A similar method was used to examine the volatile compounds associated with hydrolyzed soy proteins (Manley and Fagerson, 1970). Takahashi et al (1979) and Maheshwari et al (1997) demonstrated that treating aqueous extracts of soy flour with aldehyde oxidase produced a reduction in the beany odor of these extracts and selected aldehydes were reduced. The contribution of individual aldehydes to the overall beany odor was not demonstrated by either investigation. Kobayashi et al (1995) analyzed solvent extracts of uncooked-soaked and ground soybeans by gas chromatography/olfaction (GCO), GC/mass spectrometry (MS) and aroma extract dilution analysis. They concluded that the main contributors to the odor of uncooked-soaked and ground soybeans (in order with the strongest first) were trans,trans-2,4-nonadienal, trans,trans-2,4-decadienal, hexanal, 2-pentyl furan, 1-octen-3-one, trans-2-nonenal, an unidentified compound and trans,cis-2,4-nonadienal. Because soymilk is typically heated to deactivate the lipoxygenase, other degradative enzymes and trypsin inhibitors, these findings have limited application to soymilk. Torres-Penarada and others (1998) demonstrated a reduction of cooked beany odor and flavor in soymilk made from lipoxygenase-free soybeans.
Boatright and Crum (1997) analyzed the lipid extracts from xe2x80x9cdryxe2x80x9d commercial SPIs by GCO and GC/MS. The strongest identified odor compounds (in order of strongest first) were butyric acid, 2-methyl butyric acid methyl ester, 2-pentyl pyridine and hexanal. The mean content of 2-pentyl pyridine in commercial soy protein isolates is 54,000 times above its flavor threshold (0.000012 ppm) and contributes an extremely repulsive flavor profile (described as having a throat-catching taste and a grassy odor by our sensory panelists). This is the highest reported flavor value of any compound found in soy protein products and the first reported occurrence of 2-pentyl pyridine in a soy product.
Other compounds that have been thought to contribute to the taste of soy products include a report that phenolic acids might contribute to the bitter/astringent characteristic of soy (Arai et al, 1966). Subsequent investigations by Rackis et al (1967) and Maga and Lorenz (1974) indicated that the level of combined phenolic acids in soybean flour is close to their synergistic flavor threshold level of 40 to 90 parts per million (ppm). Subsequent processing modifications that substantially reduced the level of phenolic acids in SPI resulted in no significant improvement in the bitter/astringent flavor properties of SPI (How and Morr, 1982).
An investigation of the undesirable flavor components extracted from whole soybean meal with 70% ethanol (Okubo et al, 1992) concluded that the soy saponins and isoflavones contributed to the bitterness and astringency of whole soybeans, of which soy saponin A made the strongest contribution. This investigation reported flavor thresholds and profiles (in water) for many soy saponins and isoflavones. The level of total saponins in soy protein isolates was previously determined to be 0.76% (Ireland et al, 1986) with approximately one-sixth of these being soy saponin A (Ireland and Dziedzic, 1986). Since the level of soysaponin A in SPI is approximately 1000 times above its reported flavor threshold, it likely contributes to the bitter/astringent characteristic of SPI.
Oxidized phosphatidylcholine (PC) in aqueous suspensions was reported to develop a bitter taste (Sessa et al, 1974) with a flavor threshold value of 0.006% (Sessa et al, 1976). Since defatted soy flakes contain approximately 0.08% (a flavor value of 13), oxidized PC was proposed to contribute to the bitterness in soy protein products. These conclusions are in disagreement with the findings of Honig et al (1969) which reported no such flavors associated with the phospholipids from defatted soy flakes.
Methanethiol has been shown to be a primary contributor to halitosis (bad breath) in humans (Yasuda et al, 1996). Dimethyl trisulfide, methanethiol and xcex2-ionone have been reported to be major contributors to the offensive odors formed when broccoli florets were stored under reduced-oxygen conditions (Hansen et al, 1992). Chin and Lindsay (1994a) demonstrated that DMTS could be formed from methanethiol in the presence of transition metals and ascorbate. Another proposed mechanism for DMTS formation in Brassica vegetables (including broccoli) involves the conversion of S-methylcysteine sufoxide to sulfenic acid (by the action of cystine lyase) with subsequent dimerization to methyl methanethiosufinate (Marks et al, 1992). The sulfinate could then react rapidly with hydrogen sulfide to form DMTS. The reaction of methyl methanethiosulfinate and methyl methanethiosulfonate with hydrogen sulfide to form DMTS in model systems has been confirmed by Chin and Lindsay (1994b) and was proposed to be the prominent mechanism for the formation of methanethiol and DMTS in Brassica vegetables.
Citation of the above documents is not intended as an admission that any of the foregoing is pertinent prior art. All statements as to the date or representation as to the contents of these documents is based on subjective characterization of information available to the applicant, and does not constitute any admission as to the accuracy of the dates or contents of these documents.
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It is therefore an object of the present invention to provide soy products, especially food items with less offensive odor and flavor.
It is a further object to provide methods to produce soy products, especially food items that comprise soy products, wherein the soy products result in less offensive odor and flavor.
Definitions
xe2x80x9cSoybean(s)xe2x80x9d or xe2x80x9csoyxe2x80x9d or xe2x80x9csoy product(s)xe2x80x9d means any soybean based product, including, but not limited to, whole soybeans, soybean pieces, soy meal, soybean flour, soybean milk, soy protein concentrate, soy protein isolate, etc.
The xe2x80x9cphenolic compoundsxe2x80x9d, include compounds having one or more of phenolic hydroxyl groups and which reduce offensive soy odor. The term xe2x80x9cphenolic hydroxyl groupxe2x80x9d used herein stands for a hydroxyl group directly bonded to an aromatic ring like the benzene ring. The aromatic ring may be any of benzene, pyridine, thiophene, naphthalene, biphenyl, benzoic acid, catechins and other aromatic rings which have a structure that can be converted into ketones by oxidation of hydroxyl groups. Benzene ring is most preferred.
Moreover, for the purposes of the present invention, the term xe2x80x9caxe2x80x9d or xe2x80x9canxe2x80x9d entity refers to one or more of that entity; for example, xe2x80x9ca deodorant compoundxe2x80x9d or xe2x80x9can extractxe2x80x9d refers to one or more of those compounds or at least one compound. As such, the terms xe2x80x9caxe2x80x9d (or ""anxe2x80x9c), xe2x80x9cone or morexe2x80x9d and xe2x80x9cat least onexe2x80x9d can be used interchangeably herein. It is also to be noted that the terms xe2x80x9ccomprisingxe2x80x9d, includingxe2x80x9d, and xe2x80x9chavingxe2x80x9d can be used interchangeably. Furthermore, a compound xe2x80x9cselected from the group consisting ofxe2x80x9d refers to one or more of the compounds in the list that follows, including mixtures (i.e. combinations) of two or more of the compounds. According to the present invention, an isolated or biologically pure, molecule is a compound that has been removed from its natural milieu. As such, xe2x80x9cisolatedxe2x80x9d and xe2x80x98biologically purexe2x80x99 do not necessarily reflect the extent to which the compound has been purified. An isolated compound of the present invention can be obtained from its natural source and partially purified such that other components remain present in the mixture, or can be produced using molecular biology techniques or can be produced by chemical synthesis.